NATURE OF OPERATIONS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Variable Interest Entities (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Variable Interest Entity [Line Items]
Media revenues	$ 679,290	$ 666,534	$ 1,329,225	$ 1,245,423
Income from equity and cost method investments	1,462	943	141	1,366
Eliminations
Variable Interest Entity [Line Items]
Media revenues	(21,010)	(23,020)	$ (40,170)	(41,493)
Consolidated VIEs, aggregated
Variable Interest Entity [Line Items]
Initial term of certain outsourcing agreements			5 years
Consolidated VIEs | Eliminations
Variable Interest Entity [Line Items]
Liabilities associated with the certain outsourcing agreements and purchase options	76,700		$ 76,700		$ 74,500
Consolidated VIEs | Cunningham | Eliminations
Variable Interest Entity [Line Items]
Total payments made under the LMA excluded from liabilities	42,400		42,400		40,800
Total capital leased liabilities excluded from VIE consolidation	4,500		4,500		4,500
VIEs which are not primary beneficiary
Variable Interest Entity [Line Items]
Carrying amount	109,000		109,000		$ 117,000
Income from equity and cost method investments	$ 3,800	$ 900	$ 3,500	$ 1,200